This invention refers to a method and an apparatus suitable for feeding a polyurethane mixture to form thermally insulating layers into cavities of hollow bodies extending in a horizontal plane, providing a thermally insulating polyurethane foam for example into the hollow walls of refrigerator cabinets, household or industrial freezers, display counters or insulating panels, normally used in the building field, for cold-storage cells, or for other similar applications.
As known, polyurethane foams have several typical properties: in particular, the reaction between the polyurethane components, such as a polyol and an isocyanate, tends to develop heat and CO2 gas, and cause the release of a foaming agent to generate a foam which rapidly expands, flowing into the cavity of a hollow body to fill it completely.
Polyurethane foams are also the best industrially available thermal insulating materials and are usable for all those applications for which polyurethane foam, in addition to forming a necessary thermally insulating layer, contributes to provide mechanical characteristics to a manufactured articles. These are the reasons why polyurethane foams are mainly used in the manufacture of refrigerator cabinets, freezers, thermally insulating panels and for other similar uses.
A hollow body, such as a refrigerator cabinet, a panel, usually comprises two opposite shells or plates which, in their assembled condition provide a cavity into which a metered quantity of a polyurethane mixture is injected; usually the polyurethane mixture is injected into the cavity of the hollow body laying into a horizontal plane, such as the back wall of a refrigerator cabinet on a support pallet of a foaming plant; the cabinet is supported in a so called “top open mouth” that is with the back wall resting on the horizontal pallet and the openings for the cabinet doors, facing upwards. Once injected, the polyurethane mixture chemically reacts and expands to form a foam which runs and rises into the cavity of the hollow body filling it completely; this technology is normally known as “RIM” or “Reaction Injection Molding”.